GB1122031A - Photometric apparatus - Google Patents

Abstract

1,122,031. Photo-electric measurements. NATIONAL RESEARCH DEVELOPMENT CORP. Nov. 11, 1965 [Nov. 11, 1964], No. 46057/64. Heading G1A. The transmissive and reflective properties of a test sample in comparison with a reference sample are determined by alternately moving the test and reference samples into and out of a single light beam between a single source and detector and a measurement value is derived either by bringing to equality the test and reference electrical signals produced by the detector during the test and reference phases or by measuring the ratio of these electrical signals. The signals may be brought to equality either by attenuating them directly or by reducing the intensity of the light beam whilst either the test or reference sample is illuminated with a variable aperture shutter or a variable time of opening shutter. The final electrical measurement-valve signal may operate a recorder or control an industrial process. The samples may be mounted on a wheel or reciprocating slide whose movements may be continuous, or step-wise to momentarily hold the samples stationary in the beam. The wavelength of the light may be varied by using a variable output monochromator or filters. Fig. 10 shows a unified optical arrangement for determining direct, diffuse or total transmissive and reflective properties and also luminance factors. It comprises two integrating spheres IS1, IS2, two wheels W1, W2 for supporting the reference and test samples RS, TS, of which liquids are mentioned, and four photo-cells PC1 to PC4 covered by diffusing screens DS1 to DS4. Using the integrating sphere IS1 and wheel W2 the direct reflective factor is determined using PC4, the light paths for which are shown, and the diffuse and total reflective factors determined using PC2 with the cap C (shown dotted in Fig. 10) blocking off PC4 and internally painted either black or white respectively. The equivalent transmission factors are determined using integrating sphere IS1, photo-cells PC1 and PC3 and wheel W2, but with wheel W1 and integrating sphere IS2 removed. The luminance factor, for which light is directed at 45 degrees on to the sample which is then viewed in a normal direction, is determined using wheel W1 and photo-cell PC4 with wheel W2 and integrating sphere IS2 removed; a prism placed after lens CL directs light away from prism PC2 and at 45 degrees to the right hand side of the wheel W1 as viewed in Fig. 10. The inverse luminance factor, which is vice-versa of the above luminance factor, uses wheel W1 and photo-cell PC4, the prism PC2 now directing light normally on to the sample and PC4 receives light reflected at 45 degrees.